\begin{tikzpicture}
    \tkzDefPoints{0/0/B, 2/0/C, 2/3/A}

    \tkzDrawPolygon(A,B,C)
    \tkzMarkRightAngle(A,C,B)
    \tkzLabelPoints[above](A)
    \tkzLabelPoints[below](B,C)
\end{tikzpicture}

